Thiolate Ligands as a Double-Edged Sword for CO Oxidation on CeO2 Supported Au25(SCH2CH2Ph)18 Nanoclusters

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• 作者：Zili Wu ; De-en Jiang ; Amanda K. P. Mann ; David R. Mullins ; Zhen-An Qiao ; Lawrence F. Allard ; Chenjie Zeng ; Rongchao Jin ; Steven H. Overbury
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：April 23, 2014
• 年：2014
• 卷：136
• 期：16
• 页码：6111-6122
• 全文大小：546K
• 年卷期：v.136,no.16(April 23, 2014)
• ISSN：1520-5126

文摘

The effect of thiolate ligands was explored on the catalysis of CeO₂ rod supported Au₂₅(SR)₁₈ (SR = 鈭扴CH₂CH₂Ph) by using CO oxidation as a probe reaction. Reaction kinetic tests, in situ IR and X-ray absorption spectroscopy, and density functional theory (DFT) were employed to understand how the thiolate ligands affect the nature of active sites, activation of CO and O₂, and reaction mechanism and kinetics. The intact Au₂₅(SR)₁₈ on the CeO₂ rod is found not able to adsorb CO. Only when the thiolate ligands are partially removed, starting from the interface between Au₂₅(SR)₁₈ and CeO₂ at temperatures of 423 K and above, can the adsorption of CO be observed by IR. DFT calculations suggest that CO adsorbs favorably on the exposed gold atoms. Accordingly, the CO oxidation light-off temperature shifts to lower temperature. Several types of Au sites are probed by IR of CO adsorption during the ligand removal process. The cationic Au sites (charged between 0 and +1) are found to play the major role for low-temperature CO oxidation. Similar activation energies and reaction rates are found for CO oxidation on differently treated Au₂₅(SR)₁₈/CeO₂ rod catalysts, suggesting a simple site-blocking effect of the thiolate ligands in Au nanocluster catalysis. Isotopic labeling experiments clearly indicate that CO oxidation on the Au₂₅(SR)₁₈/CeO₂ rod catalyst proceeds predominantly via the redox mechanism where CeO₂ activates O₂ while CO is activated on the dethiolated gold sites. These results point to a double-edged sword role played by the thiolate ligands on Au₂₅ nanoclusters for CO oxidation.